Groundwater flowing through a complex system of fractures within the Trinity Aquifer emerges as an artesian spring known as Jacob's Well. The once-fountaining water, at a near-constant temperature of 68 degrees, provides the majority of the flow to Cypress Creek in the Wimberley Valley. From the 12-foot diameter opening, the main shaft descends to a depth of 20 feet before extending into four water-filled caverns. At one mile in length, Jacob's Well is the second-largest submerged cave system in Texas. It provides habitat for many species of fish, turtles, aquatic invertebrates and amphibians, such as the fern bank salamander. Described as a natural wonder in an 1858 newspaper article by Texas land agent, Jacob de Cordova, Jacob's Well is still known as one of the state's most mysterious and beautiful geological features. For thousands of years, the cool clear spring waters have attracted humans, from Native Americans to European pioneers. In 1996, to protect against development that could reduce the well's flow and threaten its very existence, local landowners formed the Wimberley Valley Watershed Association. They created the 81-acre Jacob's Well Natural Area, which became Hays County's first nature preserve. Jacob's Well lured early scuba divers who wished to explore and map it. Reputed to be one of the most dangerous places on earth to dive, it claimed the lives of at least eight divers. As a result, only specially trained divers are allowed into the caverns to measure and monitor conditions. Despite the restricted access for security reasons, Jacob's Well Natural Area remains a popular recreational and ecological destination in Texas.